In the case of a known contractile drive disclosed in the German patent publication 10,034,389 A1 a contractile hose extends between two head pieces which are respectively provided with two clamping units and which are screwed together like a gland nut. Between the clamping units an annular clamping gap is defined, in which the contractile hose is clamped at its associated end region. If the internal space of the contractile hose is charged with a pressure medium subject to a certain actuating pressure, the contractile hose will expand radially and will simultaneously pull the two head pieces toward one another. It is in this manner that it is possible for external structures or, respectively, components, which are fixed on the force output means of the head pieces, to be moved relatively toward each other and/or clamped together.
In the case of the known contractile drive there was the problem that owing to its liability to deformation the contractile hose could be pulled out of the clamping gap. Therefore the two clamping units were designed to be adjusted in the longitudinal direction of the contractile drive and the tightening faces were so contrived that owing to frictional effects between them and the contractile hose a certain entraining effect is produced with the result that on actuation of the contractile hose there is an automatic reinforcement of the gripping or clamping action between the two clamping units.
It has however now been discovered that there are still certain shortcomings with the known clamping attachment, which are more particularly significant at raised temperatures or in the case of the use of relatively soft hose materials. The material then tends to creep and in the worst case the contractile hose may slip out of the head piece completely.